The present invention relates to a magnetoresistive element whose electrical resistance changes due to an external magnetic field and also to a magnetic device using the same, for example, a magnetic sensor used for detection of magnetic signals and a memory device used for storage of magnetic signals.
With respect to magnetoresistive elements, an element using an anisotropic magnetoresistive (AMR) effect as well as a giant magnetoresistive (GMR) element using a change in resistance that depends on the relative angle of magnetization between magnetic layers laminated alternately via nonmagnetic layers are already in practical use. Furthermore, research has been conducted with regard to a tunnel magnetoresistive (TMR) element using the dependence of tunneling current between magnetic layers on the relative angle of magnetization. This element has a three-layer structure in which an extremely thin insulating barrier layer is interposed between two magnetic layers.
A rate of change in magnetoresistance of a TMR element depends on the spin polarizability of a magnetic material. Therefore, as spin polarizability of a magnetic substance increases, a larger rate of change can be obtained. Metal magnetic substances such as iron or cobalt have spin polarizability of about 50% at most, and this polarizability imposes a limitation with respect to the rate of change in the magnetoresistance of the element. Thus, as materials having greater spin polarizability, oxide magnetic materials containing transition metals are expected to be used. For example, perovskite structure materials such as LaMnO3, particularly materials having a double perovskite structure, exhibit high spin polarizability even at room temperature. JP2000-174359A discloses a magnetoresistive element containing an oxide with a double perovskite structure.
However, there is a problem with using a perovskite structure material for operation at a high temperature, since the magnetic transition temperature is low. A double perovskite structure material does have a higher magnetic transition temperature, but it is still about 200xc2x0 C., so that consideration must be given to a rise of temperature of the element at the time of operation. On the other hand, an oxide having a spinel crystal structure has a magnetic transition temperature of 400xc2x0 C. or higher. As a TMR element using a spinel-type magnetic substance, a three-layer laminated tunnel junction element has been reported in which a magnetite (Fe3O4) thin film magnetic layer is used (X. W. Li et al., Applied Physics Letters, Vol. 73, No. 22, P. 3282-3284, published in 1998). However, a rate of change in magnetoresistance that can be obtained from a TMR element using a spinel-type magnetic substance conventionally stays within several percent, which is smaller than expected from the spin polarizability. The reason therefor is not known in detail, but it is considered that various properties centering the electronic state of a spinel-type magnetic layer are not sufficient, so that the spin hops at random, thereby reducing the apparent spin polarizability.
A spinel-type magnetic substance has a complicated crystal structure compared to ordinary metals or alloyed magnetic materials. Therefore, it is not easy to obtain a good-quality spinel-type magnetic layer by controlling the crystallographic, electrical and magnetic properties appropriately. In order to form a good-quality spinel-type magnetic layer, a high-precision facility and highly advanced technology are required. Furthermore, the production is complicated, and the reproducibility also is difficult. Under such circumstances, a sufficient change in magnetoresistance was not yet obtained from an element using a spinel-type magnetic substance.
Therefore, it is an object of the present invention to improve a magnetoresistive element using a spinel-type magnetic substance.
It has been found that a larger magnetoresistive effect can be obtained by interposing a titanium nitride (TiN) layer between a substrate and a spinel-type magnetic substance. In other words, a magnetoresistive element of the present invention has a substrate and a multilayer film formed on the substrate, and this multilayer film includes a first magnetic layer, a nonmagnetic layer formed on the first magnetic layer and a second magnetic layer formed on this nonmagnetic layer, the layers being laminated from a side of the substrate in this order. An electric current is supplied in a direction perpendicular to a film surface of the multilayer film, and a change in electrical resistance is detected by the electric current based on a change in a relative angle between a magnetization direction of the first magnetic layer and a magnetization direction of the second magnetic layer. The first magnetic layer has a spinel crystal structure, and the multilayer film further includes a titanium nitride layer interposed between the substrate and the first magnetic layer.
According to the present invention, it is comparatively easy to obtain an excellent junction even by using a magnetic substance having a spinel crystal structure. This excellent junction results from the interposed titanium nitride layer itself, so that there is also an advantage of not necessarily using particularly high-precision equipment for production of the element.
By using the element of the present invention, the properties of various magnetic devices such as a magnetic sensor or a magnetic memory device can be improved. One example of the magnetic sensor is a magnetoresistive effect type head.